Beginning with the increase in energy costs of the seventies, all manner of devices have been developed for burning wood, used engine oil, paper, animal fat and everything else that is combustible, for use particularly in backwoods areas where such materials are readily available. At the same time, in conjunction with these furnaces, stoves and ovens, many devices are marketed which either actively or passively increase the circulation of hot air from a fireplace out into the room in which the fireplace is situated to increase the efficiency of space heating from a fireplace, which in its natural state is rather low.
The above-mentioned systems, which run pipes through the firepit area of a fireplace and are active, generally have an electric motor driving a fan or blower which causes the air to circulate through the firepit and back out into the open area. This is quite an effective system and greatly enhances the heating effect of a fireplace. Rooms which were previously warm only near the firepit can now be warmed throughout due to the convection effects of these devices.
However, because these active systems uniformly rely on an external supply of energy, i.e. electricity, they are obviously not as versatile as they would be otherwise. Although the electricity used to drive the blower motor may not be significant in terms of energy consumption compared to the heat of the fire which is transferred into the room, the fact that electricity is required has two serious drawbacks. Principally, the unit cannot be used in backwoods areas that do not have utilities. Secondarily, in the event of a blackout, which some people fear considerably, or a massive failure of the nations's energy supply system, the unit would be ineffective when it is needed most. There is a need, therefore, for such a unit, capable of creating hot air convection into a room, which is independent of electricity or other external energy source, but draws on the fire itself to produce an active circulation effect.